Karyomorphology of Corylopsis Glabrescens and C. Gotoana Endemic to Japan (Hamamelidaceae; Hamamelidoideae)

Karyomorphology of Corylopsis glabrescens and C. gotoana endemic to Japan (Hamamelidaceae; Hamamelidoideae)

Yoshiko Kono1,2, Masahisa Okada3, Hiroaki Setoguchi4 and Kazuo Oginuma5,6

1Graduate School of Human Health Science, Kochi Women’s University, Eikokuji-cho 5-15, Kochi 780-8515, Japan; 2Research Center for Biodiversity, Academia Sinica, Taipei 115, Taiwan; 3Kochi Agricultural Research Center, Amaeda 1100, Nankoku 783-0023, Japan; 4Deparment of Biology, Graduate School of Human and Environmental Studies, Kyoto University, Yoshida Nihonmatsu-cho, Sakyo-ku, Kyoto 606-8501, Japan; 5Department of Environmental Science, Faculty of Human Life and Environmental Science, Kochi Women’s University, Eikokuji-cho 5-15, Kochi 780-8515, Japan

6Author for correspondence: ([email protected]) Received May 10, 2008; accepted July 21, 2008

ABSTRACT. Chromosome numbers and karyotypes of Corylopsis glabrescens and C. gotoana in the Hamamelidaceae were investigated. Corylopsis glabrescens was diploid with 2n=24=14m+8sm+2st, while C. gotoana was tetraploid with 2n=48=36m+8sm+4st. The karyotype of the diploid C. glabrescens was different from that of the diploid C. pauciflora previously reported in Japan, suggesting a heterogeneous origin of the two species. The karyotype of the tetraploid C. gotoana seemed to share a homogeneous karyotype composition with the hexaploid C. spicata previously reported in Japan.

KEYWORDS: Chromosome number, Corylopsis, Hamamelidaceae, karyotype

Plants of Corylopsis, the Hamamelidaceae are small JP2702) and that of C. gotoana was collected in Nantan deciduous trees that tend to grow at forest edges on rocky City, Kyoto Prefecture, Japan (Voucher: H. Setoguchi terrain in mountains or gorges of the warm temperate JP2701). Somatic chromosomes were examined in zone. This genus comprises 26-29 species that are widely meristematic cells of their young leaves. The methods of distributed in the Sino-Japanese region (Yamazaki 1989; pretreatment, fixation and staining followed Oginuma et Mabberley 1997; Hsieh 2003; Zhang and Zhang 2003) al. (1992). Terminology of chromosome morphology on from the Himalayas, China, Taiwan, Korea to Japan. the basis of the position of the centromeres followed Four species of the genus such as C. spicata Sieb. et Levan et al. (1964). Voucher specimens were deposited Zucc., C. pauciflora Sieb. et Zucc., C. gotoana Makino, in the Herbarium of Kyoto University (KYO). and C. glabrescens Franch. et Savat. are found in the western part of the islands in the Japanese Archipelago in RESULTS AND DISCUSSION the eastmost distribution of the genus. Corylopsis spicata, Chromosome number and karyotype of C. glabrescens C. gotoana and C. glabrescens are endemic to Japan, The chromosome number of C. glabrescens was firstly while C. pauciflora also occurs in the high mountains of reported as n=24 (Santamour 1965) that might be of Taiwan as well as Japan. tetraploid if the basic chromosome number was decided Eight species of Corylopsis showed the chromosome to be x=12. In contrast, our present observation showed numbers of n=12, 24, 36, and 2n=24 and 2n=72, that 2n=24 for this species that could be diploid. Thus, the suggested a polyploid series with the basic chromosome diploid chromosome number of 2n=24 for this species number of x=12 (Anderson and Sax 1935; Santamour was reported here for the first time. The chromosome 1965; Mehra and Khosla 1969, 1972; Mehra 1976; lengths of the chromosome complement (2n=24) in this Oginuma 1991; Oginuma and Tobe 1991). Among the species studied at mitotic metaphase gradually varied Japanese species, only C. pauciflora (2n=24) and C. from 1.4-0.8 µm. Among the 24 chromosomes, 14 had spicata (2n=72) have reported their karyotypes (Oginuma the centromere at median position (m), eight had the 1991; Oginuma and Tobe 1991). centromere at submedian position (sm) and two had the Karyomorphological characters of C. glabrescens and centromere at subterminal position (st) (Figs. 1 and 2). C. gotoana are here studied and discussed on the trend in The secondary constriction was (sc) observed in the chromosome diversity and speciation of this genus. interstitial region of the long arm of a pair of submedian centromeric chromosomes (arrowheads in Figs. 1 and 2). (sc) MATERIALS AND METHODS Thus, the karyotypic formula was 2n=24=14m+8sm +2st. A plant of C. glabrescens was collected in Tenkawa- mura, Nara Prefecture, Japan (Voucher: H. Setoguchi Chromosome number and karyotype of C. gotoana

27 28 KONO ET AL.

Figs. 1-4. Somatic chromosomes at metaphase of two species of Corylopsis. 1 and 2. Corylopsis glabrescens (2n=24); 3 and 4. C. gotoana (2n=48). 2 and 4. Hand drawings of the respective preceding photographs. Large arrows indicate chromosomes with centromeres at submedian positions. Small arrows denote chromosomes with centromeres at subterminal positions. Arrowheads show chromosomes with a secondary constriction. Scale bar=2 µm.

The chromosome number of C. gotoana was 2n=48 that 24=14m+8sm+2st. The compositions of the chromosome could be tetraploid after the basic chromosome number types regarding the centromeres at the median, submedian of x=12. The finding of a tetraploid of 2n=48 for this and subterminal positions were 50.0%, 16.7%, and species was reported here for the first time. The 33.3% respectively in C. pauciflora and 58.3%, 33.3%, chromosome lengths of the chromosome complement and 8.3% respectively in C. glabrescens. Thus, the two (2n=48) in C. gotoana studied at mitotic metaphase diploid species had mutually heterogeneous karyotypes. gradually varied from 1.1-0.7 µm. Among the 48 Therefore, these two diploid species might have been chromosomes, 36 had the centromere at median position, derived from different ancestors. eight had the centromere at submedian position, and four The karyotype of C. gotoana (tetraploid) in the present had the centromere at subterminal position (Figs. 3 and study was 2n=48=36m+8sm+4st, while that of C. spicata 4). No sat-chromosome was observed. Thus, the karyotypic (hexaploid) in the previous study was 2n=72=54m+ formula was 2n=48=36m+8sm+4st. 12sm+6st (Oginuma 1991). The chromosome compositions represented by the positions of median, submedian and Implications for the phylogenetic relationships among subterminal centromeres in the two species were 75.0%, the Japanese species of Corylopsis The present study 16.7% and 8.3%, respectively. Thus, C. gotoana (2n=48) suggested that the Japanese Corylopsis comprised two and C. spicata (2n=72) might be originated from a diploid species (2n=24; C. glabrescens and C. pauciflora), diploid with the same frequencies of chromosome types. one tetraploid (2n=48; C. gotoana), and one hexaploid For instance, the karyotype origin could be speculated as species (2n=72: C. spicata). However, the two diploid 2n=24=18m+4sm+2st which has not been discovered species possessed heterogeneous karyotypes, whereas the yet. In contrast, another possibility could be that C. tetraploid C. gotoana and the hexaploid C. spicata spicata (2n=72) might be derived from fertilization showed very similar chromosome composition to each between a normal gamete with n=24 and an unreduced other. gamete with n=48 such as that of C. gotoana (2n=48) or The karyotype of C. pauciflora was reported previously its allied tetraploid. to be 2n=24=12m+4sm+8st (Oginuma and Tobe 1991). A recent phylogeographic study resulted that 60 The karyotype of C. glabrescens in this study was 2n= individual plants from nine populations of C. gotoana KARYOMORPHOLOGY OF CORYLOPSIS GLABRESCENS AND C. GOTOANA (HAMAMELIDACEAE) 29 examined from Kyoto to Shimane Prefectures in Western Mehra, P. N. and Khosla, P. K. 1969. In: IOPB chromosome Honshu, Japan and 41 individuals from six populations number reports. Taxon 18: 213-221. Mehra, P. N. and Khosla, P. K. 1972. Cytogenetical studies of in C. spicata in Kochi Prefecture, Shikoku District, Japan East Himalayan Hamamelidaceae, Combretaceae and had common single chloroplast DNA haplotype and ITS Myrtaceae. Silvae Genet. 21: 186-190. genotype, while the other species had different types of Oginuma, K. 1991. Karyomorphology of Corylopsis spicata cpDNA and ITS (Yamanaka et al. in press). These (Hamamelidaceae; Hammeidoideae). Acta Phytotax. 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